In the field of medical imaging, various systems have been developed for generating medical images of various anatomical structures of individuals for the purpose of screening and evaluating medical conditions. These imaging systems include, for example, computed tomography (CT) imaging systems, magnetic resonance imaging (MRI) systems, X-ray systems, ultrasound systems, positron emission tomography (PET) systems, and single photon emission computed tomography (SPECT) systems, etc. For example, computed tomography (CT) imaging systems can be used to acquire a volumetric dataset of cross-sectional images or two-dimensional (2D) “slices” that cover an anatomical part. Each imaging modality may provide unique advantages over other modalities for screening and evaluating certain types of diseases, medical conditions or anatomical abnormalities.
The acquired images are reviewed to identify any lesions, medical conditions or abnormal anatomical structures, such as cancer, polyps, etc. One conventional method of review is by manually looking at hard copies (e.g., X-ray films, prints, photographs, etc.) of the acquired images to discern characteristic features of interest. For example, a trained radiologist may view a film image attached to a light board to identify potential abnormal anatomical structures or lesions. However, such manual review process is very time consuming and prone to human error.
To assist interpretation of medical images, various visualization systems and tools have been developed. The acquired images are typically digitized for viewing directly on viewing stations, either as part of an electronic picture archiving and communication (PAC) system, standalone workstations or even communication devices (e.g., phones, personal digital assistants, etc.). Commonly used methods to view these datasets include two-dimensional (2D) or slice-by-slice viewing, and three-dimensional (3D) viewing. For cases involving hollow or tubular structures (e.g., airways, colon, blood vessels, etc.), such visualization typically tries to simulate the real inspection of the desired structure and is commonly referred to as a virtual flythrough.
In the 2D or slice-by-slice viewing mode, the 2D images are rendered by projecting volumetric data along principal orthogonal directions onto an axial, coronal or sagittal viewing plane. The user typically browses through numerous 2D images in search of abnormal structures or medical conditions by manually scrolling up and down a stack of axial images following a mental image of the anatomical structure. Although the 2D reading mode is most commonly used in clinical radiological review, inherent limitations do exist. For example, abnormal structures are often easily missed because they are usually not visible in most of the 2D images and appear only very subtly. In the context of virtual colonoscopy (e.g., CT colonography) for colon cancer screening, for instance, polyps are often missed since they appear or disappear very quickly in the scrolling process. In addition, 2D images reconstructed along planes (or axes) other than the original acquisition plane are often better suited for visualizing a given abnormality.
As an alternative visualization means, the 3D viewing mode also presents another set of inherent limitations. For example, 3D sequences of images of an anatomical structure based on a pre-defined path have many limitations because the path is not always correct or feasible to compute due to occlusions or collapsed areas. In addition, the 3D view is often too narrow and provides little contextual information. Further, anatomical features of interest are often occluded by surrounding tissues or occluding material. For instance, in a virtual colonoscopy, polyps are often partially occluded by haustral folds, fluid and/or fecal material.
To address field-of-view limitations, the viewing angle can be expanded to present a broader panoramic view. Alternatively, the visibility can be expanded with bidirectional angles. As for limitations due to partial occlusion, these can be addressed by virtually unfolding the anatomical structure (e.g., colon) into a tubular structure and cutting it open to present a filet view. The virtual flythrough can be performed over the open structure or a curvy reconstruction of the tubular structure. These mechanisms, however, introduce much distortion and can be extremely ill-suited in most cases where the colon is not extremely well-distended, clean or insufflated. In addition, these methods require intensive real-time interactive capabilities as well as 3D rendering resources, which can limit their feasibility and deployment into viewing environments that are inherently 2D.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for more efficient, effective, and enhanced systems and methods for reviewing medical image data.